The present invention concerns a process for the selective deprotonation and functionalization in the 2-position of certain 3-substituted benzotri-fluorides.
U.S. Pat. No. 5,858,924 describes certain substituted benzenesulfonamide compounds and their use as herbicides. U.S. Pat. No 5,272,128 discloses certain phosphonosulfonate compounds and their use as herbicides. 2-Substituted-6-(trifluoromethyl)benzene-sulfonyl chlorides are useful intermediates for the preparation of these herbicides.
In U.S. Pat. No. 5,272,128, 2-methoxy-6-(trifluoromethyl)benzenesulfonyl chloride is prepared in an 82/18 ratio with 2-methoxy-4-(trifluoromethyl)-benzenesulfonyl chloride by deprotonation of 3-(trifluoromethyl)anisole with n-butyl lithium followed by quenching with sulfur dioxide and treatment of the resulting lithium sulfinate with sulfuryl chloride.
In U.S. Pat. No. 5,858,924, 2-propylthio-3-(trifluoromethyl)anisole is prepared in an 82/10 ratio with 2-propylthio-5-(trifluoromethyl)anisole by deprotonation of 3-(trifluoromethyl)anisole with n-butyl lithium followed by quenching with dipropyl disulfide. Subsequent treatment with chlorine produced a mixture of the corresponding sulfonyl chlorides.
It would be advantageous to produce these materials in higher yield and with better selectivity to the desired product.
The present invention concerns the highly selective deprotonation of 3-substituted benzo-trifluorides in the 2-position with alkyl lithium compounds in the presence of primary or secondary amines. The resulting 3-substituted-2-lithiobenzo-trifluorides are further derivatized or functionalized by reaction with electrophilic reagents. More particularly, the present invention concerns a process for the preparation of a 2-lithiobenzotrifluoride of Formula I 
wherein
X represents F, Cl or OR and
R represents a C1-C4 alkyl group optionally substituted with a C1-C4 alkoxy group
which comprises contacting a benzotrifluoride of Formula II 
wherein X is as previously defined
with an alkyl lithium in an inert organic solvent in the presence of a catalytic amount of a primary or secondary C1-C8 alkyl amine, wherein the molar amount of alkyl lithium is less than the sum of the molar quantities of the benzotrifluoride and of the primary or secondary alkyl amine, and equilibrating the reaction mixture. In another aspect of the present invention, the 3-substituted-2-lithiobenzotrifluorides are further contacted with an electrophilic reagent.